User:Soap/UMB

The uterine microbiome bacterium (UMB) leads women along the north coast of Repilia to miscarry male babies shortly after conception, resulting in a birth sex ratio of nearly 100% female. The rare male births are typically preceded by abnormal menstruation. These males are enough to sustain the civilization, because each man mates with dozens of women, but nonetheless the Repilian women along the coastal colonies often seek men outside their colonies for husbands. This means that almost all men in the colonies are outsiders. Since the UMB is dietary (and thus environmental), rather than genetic, these men and women see each other as kin, rather than there being a coastal lineage and an inland lineage, or likewise a tribal or racial boundary. (UMB can also stand for Uterine MicroBiome.)

Mechanism

The UMB depends on women's consumption of a microorganism in the water (probably an alga), which affects the woman's body chemistry. This organism is not the UMB organism, and a woman cannot achieve UMB growth by bathing in seawater. She is responsible for eating a seafood diet which converts the seawater organism into nutrients that maintain the uterine microbiome after each monthly flow.

Occasionally, a woman's flora will fluctuate, and announce with a modest vaginal discharge that the woman is ready to conceive a male baby. This is distinct from the menstruation of women living inland who do not have stable UMB's.

Because this algal organism is present in the water, it is a natural part of a seafood diet, and women in the core of the Repilian area easily maintain their UMB.

Effects on menstruation

An unstable UMB leads to painful or irregular menstruation, whereas a stable UMB (with or without the organism) produces normal menstruation. Repilian women are typically capable of suspending their menstrual cycles at will, so when traveling in areas where their diets are disrupted, they do not suffer the same menstrual pains as non-Repilians; this trait really is genetic, and leads to great social strife between different populations. For example, in those parts of Mevumep that overlap the alga's range, the local women have frequent menstrual pains and other abnormalities, and yet their society is viable, so women in this area resent both the societal structures that force them to stay there and the Repilian women who can turn off their menstrual cycles when they're not ready to conceive.

Geography

The core of Repilian territory is the core of the dominance of the algal trigger. Its distribution correlates well with cold water, but even the warmest areas within the central zone have higher concentrations of the alga than do the coldest areas outside the zone.